1. Technical Field
The present embodiments relate generally to the field of railroad couplers, and more specifically, to the casting of coupler throwers that results in a quality thrower.
2. Related Art
Sand casting is one of the earliest forms of casting, primarily for casting a body, knuckle and lock of a railcar coupler. Its popular use is due to its low cost and the simplicity of materials involved. A sand casting or a sand molded casting is a cast part produced through the following process: (1) placing a pattern in sand to create a mold, which incorporates a gating system; (2) removing the pattern; (3) filling the mold cavity with molten metal; (4) allowing the metal to cool; (5) breaking away the sand mold and removing the casting (also referred to as the shake-out process); and (6) finishing the casting, which may include weld repair, grinding, machining, and/or heat treatment operations.
In sand casting, the primary piece of equipment is the mold, which contains several components. The mold is divided into two halves—the cope (upper half) and the drag (bottom half), which meet along a parting line. The sand mixture is packed around a master “pattern” forming a mold cavity, which is an impression of the shape being cast. The sand is usually housed in what casters refer to as flasks, which are boxes without a bottom or lid, used to contain the sand. The sand mixture can be tamped down as it is added and/or the final mold assembly is sometimes vibrated to compact the sand and fill any unwanted voids in the mold. The sand can be packed by hand, but machines that use pressure or impact ensure even packing of the sand and require far less time, thus increasing the production rate. The pattern is removed, leaving the mold cavity. Cores are added as required, and the cope is placed on top of the drag.
In addition to the external and internal features of the casting, other features are incorporated into the mold to accommodate the flow of molten metal. The molten metal is poured into a pouring basin, which is a large depression in the top of the sand mold. The molten metal funnels out of the bottom of this basin and down the main channel, called the sprue (or down sprue). The sprue connects to a series of channels, called runners that carry the molten metal into the cavity. At the end of each runner, the molten metal enters the cavity through a gate (or ingate) that controls the flow rate and minimizes turbulence. Chambers called risers that fill with molten metal are often connected to the runner system. Risers provide an additional source of metal during solidification. When the casting cools, the molten metal shrinks and the additional material in the gate and risers acts to back fill into the cavities as needed. The molten metal that flows through all of the channels (sprue, runners, and risers) will solidify attached to the casting and must be separated from the part after it is removed. Molten metal is poured into the mold cavity, and after it cools and solidifies, the casting is separated from the sand mold.
Because the coupler thrower is a relatively small, simple part, historically this part has typically been forged, not cast.